One of the key components of any computer system is a place to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
Information representative of data is stored on the surface of the memory disc. disc drive systems read and write information stored on tracks on memory discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the memory disc, read and write information on the memory discs when the transducers are accurately positioned over one of the designated tracks on the surface of the memory disc. The transducer is also said to be moved to a target track. As the memory disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the memory disc. Similarly, reading data on a memory disc is accomplished by positioning the read/write head above a target track and reading the stored material on the memory disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc drive. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
The transducer is typically housed within the slider. The slider is a small ceramic block which is passed over the disc in a transducing relationship with the disc. The small ceramic block, also referred to as a slider, is usually aerodynamically designed so that it flies over the disc. Most sliders have an air bearing surface ("ABS") which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular fly height. The fly height is the thickness of the air lubrication film or the distance between the disc surface and the transducing head. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Disc drives include a disc stack which includes a spindle hub, one or more discs stacked on the hub and a clamp for attaching the discs to the spindle hub. Spacer rings are used to space each disc from adjacent discs or other components stacked on the spindle hub. The hub has a flange or lip which typically is located at one end of the spindle hub and contacts the surface of the first disc near the inner diameter of the disc. The disc spacer rings are generally considered part of the disc stack. The term disc stack applies to a disc drive having only one disc as well as to disc drives having more than one disc. The disc clamp provides a compressive load on the disc stack to hold the discs in place. The compressive load acts on the inner diameter of the disc or discs in the disc stack and is in a direction which is parallel to the axis of the hub. Many refer to this compressive load as an axial load since it acts in the axial direction. A spindle motor rotates the spindle hub and the disc stack. Some spindle motors are positioned entirely within the spindle hub.
Higher rotational speeds are used to increase performance of the disc drive. Higher rotational speeds also require that the disc in the disc drive have less mass as it is critical that the disc or discs spin up to a speed where the slider or small ceramic block is placed in transducing position with respect to the disc as soon as possible. Less mass is achieved by using thinner discs. In addition, thinner discs also allow for shorter disc stacks which are necessary for shorter form factor disc drives. The use of thinner discs with lower mass also enables the use of smaller spindle motors.
One problem associated with a disc stack using thinner discs is that when thinner discs are clamped they are more prone to cone or "potato chip". In other words, the discs may not be flat. To make the discs flat, a lower axial force may be used.
Lowering the axial load may produce another problem. Using a lower axial force lessens the friction force between the disc and the spacer or flange on the hub. When less friction force is present, discs that have been used to form a disc stack are more prone to shift from their original position when subjected to a radial force such as a shock load at the factory or during assembly into a computer or after the customer has received the disc drive. Movement between the disc and the rest of the stack produces many problems. The disc stack is out of balance and vibrates and causes noise. The unbalanced disc pack also stresses the bearings between the rotating portion of the hub and the spindle shaft. Stressed bearings have a shorter life which may be less than the stated life of the disc drive. Track following is difficult or next to impossible since the tracks are shifted from the position in which the original writing was performed. In other words, the tracks in a disc drive with a shifted disc are off center or nonconcentric with respect to the rest of the disc stack.
Any planar vibrations or vibrations which travel in the plane of the data surface of the disc make track following of the transducing head even more difficult. In other words, when the disc stack vibrates in a planar direction, the track to be followed will pass traserse to the tracking direction of the transducing head. The problem is magnified by the fact that the tracks are very closely spaced. In today's disc drives, track densities of 10,000 tracks per inch are common. Six tracks fit on a human hair. This problem will only get worse as time marches on since higher track densities are contemplated for the future.
Disc shift is also on the increase since more disc drives are subjected to shock loading which may result in disc shift. Portable or notebook computers now include disc drives. People drop these computers more than a stationary desktop computer. In addition, the lower axial forces also make disc shift more common from handling in during manufacture, shipping and distribution of the disc drives.
In the past, disc spacers have had essentially flat surfaces. These have worked until the axial loads used on flat disc spacers have dropped to prevent coning or other disc deformities. The friction force between the spacing ring and a disc surface is equal to the axial force multiplied by the coefficient of friction between the disc surface and the surface on the spacer. In other words, the friction force is directly proportional to axial clamping force being applied. Since axial clamping forces are being reduced, the friction force is also being reduced.
Thus, there is a need for a method and apparatus for use in a disc stack that produces a higher coefficient of friction between the spacer ring and the disc surface so that a higher friction force can be produced between the disc and the spacer for a given axial clamping force. The friction force would then be higher so that the disc or discs in the disc stack do not shift with respect to the hub. There is also a need for an apparatus that can be used in current methods for forming a disc stack. Furthermore, there is need for an apparatus that is easy to assemble and easy to manufacture. There is also a need for a apparatus which does not generate particles.